Fried fish with corn sauce is a common dish in Cantonese restaurants. At the inexpensive places, you’ll get fried frozen fillets with a cloying, too-thick creamed corn sauce straight out of a can. Occasionally, however, at upmarket restaurants, you can find delicious versions made with fresh fish (the best I ever had was emperor fish) in a light breading (or batter) and house-made corn sauce.
Buy whatever mild white-fleshed fish is freshest in the market. You can either fry and serve the fillets whole (which seems more formal), or cut them into strips about 2.5cm (1 inch) wide.
One of the best versions of this dish I've tasted had an unusual coating - fine rice vermicelli that had been broken into small pieces, then mixed with flour and cornstarch; when fried, the vermicelli becomes very crisp. Uncooked rice vermicelli is so brittle you can crush it just by squeezing it. It has a tendency to fly all over the place, though. To prevent this, put the vermicelli in a large, clean bag (to contain the mess), then put your hand in the bag and crush the contents.
Make the corn sauce first. Put the kernels in a pan with 400ml (1⅔ cups) of water and about one teaspoon of salt. Bring to the boil and cook until the corn is tender. Remove about half of the kernels and roughly purée them with a blender or food processor. Pour the puréed corn back into the pan with the whole kernels and water, then add the red vinegar and stir well. Taste the corn and, if needed, mix in 5g (1tsp) of sugar, or to taste.
Heat the mixture until simmering. Mix the cornstarch with 30ml (2 tbsp) of cold water, then add this to the corn and stir until the mixture thickens. Whisk the egg and drizzle it into the simmering corn mixture, stirring slowly but constantly. Simmer for about a minute, then turn off the heat.
Prepare the fish. Sprinkle salt lightly but evenly over both sides of the fish fillets. If you like, cut the fish into strips about 2.5cm (1in) wide.
Prepare the coating. Put 75g (½ cup and 4tsp) of flour into a shallow dish and mix in 1½ teaspoons of salt. Whisk the eggs in another dish. Put 50g (¼ cup and 2½ tbsp) of flour in a third dish and add the 50g (¼ cup and 2½ tbsp) of cornstarch and the crushed rice vermicelli and mix well.
Pour oil to a depth of about 1cm (7/16 in) in a skillet and heat to 170°C (340°F). Coat the fish pieces lightly but evenly with the flour/salt mixture and shake off the excess, then dip them into the egg. Dredge with the flour/cornstarch/rice vermicelli mixture, pressing on the coating to make sure it adheres. Fry the fish until it is just cooked and the coating is golden brown (one to two minutes for small pieces, eight to 10 minutes for whole fillets). Adjust the flame as needed so the temperature stays even. When the fish pieces are cooked, drain them on paper towels.
Heat the corn sauce until simmering, and if it’s too thick, stir in more water. Taste the mixture and adjust the seasonings, if needed. Ladle the corn sauce into a bowl. Mince the spring onions and scatter them on top of the sauce.
Arrange the fish on a serving plate and garnish with fresh coriander sprigs. Serve the fish with the corn sauce on the side.